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Figure 2 | Biology Direct

Figure 2

From: Evolution before genes

Figure 2

Multiple cores result in selectable attractors for a chemical network. food1-food11: food set that is assumed to be present at all times, A-H: non-food species generated by ligation/cleavage reactions. Solid lines: reactions; dotted lines: catalytic activities. Orange dotted lines show the superimposed autocatalytic loops. Structural considerations: Autocatalytic sets can contain several distinct autocatalytic units, each of which can be divided to a core of autocatalytic molecules and a periphery. Here, two independent cores are shown. The first consists of the two linked loops A → A and A → B → A. The second core includes the two linked loops C → C and C → D → E → C, with the periphery of F and G. H is the shared periphery of the two cores that requires both for its production. Dynamical considerations: This platonic reaction network can manifest in four possible stable compositions of the core-periphery units: (i) no cores (only food species); (ii) only first core (A, B; yellow area); (iii) only second core (C, D, E, F, G; blue area); (iv) both cores (all species). Now imagine that we have a compartment that only contains food species, but rare uncatalyzed reactions among them are possible. The uncatalyzed appearance of any one molecule of core species is sufficient to produce all the core species and the periphery species of that core, e.g. either A or B for the first core and either C, D, E for the second. Now let us assume that after reaching a certain size a compartment that contains both cores will split and produce propagules. If neither C, D or E is present in the daughter compartment, the second core is lost and the remaining molecules of its periphery will be washed out from the compartment. Discovering cores by rare reactions, and losing cores by segregation instability opens up the possibility for a chemical reaction network to respond to natural selection.

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